1. Field of the Invention
The present invention relates to a camera module employed in a mobile communication terminal, and more particularly, to a camera module for communicating through I2C method, in which a leakage current is prevented from being generated due to a diode provided in the camera module for interrupting overcurrent generated by the static electricity so that electric power consumption can be reduced.
2. Description of the Related Art
Generally, I2C is a two-lined bidirectional serial bus for providing communication links between integrated circuits for products manufactured in commercial quantities such as TVs, VCRs, audio equipment, and the like, and was originally proposed by Phillips Electronic Co. at first. Today, the I2C is a standard solution for embedded applications.
The I2C bus includes a serial clock line SCL for transmitting a clock and a serial data line SDA for transmitting data in serial, wherein the data is transmitted and received according to the clock. Devices connected to the I2C bus communicate as a slave with a master. The I2C is a serial bus protocol capable of communicating with a plurality of slave devices and is connected to the plurality of slave devices through a power line and the two lines SCL and SDA to transmit and receive data.
FIG. 1 is a block diagram schematically illustrating a conventional I2C bus.
Referring to FIG. 1, an I2C master device 1 is connected to a plurality of I2C slave devices 2-1 and 2-2 through the two lines of the serial clock line SCL and the serial data line SDA. The I2C master device 1, in order to control the I2C slave devices 2-1 and 2-2 for supporting the I2C, simply writes data or reads data from the I2C slaves 2-1 and 2-2 using an I2C bus controller (not shown). Moreover, the I2C master device 1 serves as a device for starting the transmission of data by generating a clock pulse and finishing the transmission, and the I2C slave devices 2-1 and 2-2 are devices addressed by the I2C master device 1. When I2C master device 1 generates a starting state, the I2C slave devices 2-1 and 2-2 connected to the I2C bus await for next data. When the I2C master device 1 transmits a slave address, the respective I2C slave devices 2-1 and 2-2 compare the transmitted slave address with their own respective addresses and an I2C slave device having its own address corresponding to the transmitted address transmits a response with respect to a continued ACK signal region. Then, the I2C master device 1 receives and transmits data from and to a corresponding I2C slave device. When the receipt and transmission of data is finished, the I2C master device 1 generates a stopping state and releases the bus. For the operation of the I2C bus, pull-up power Vdd (here, pull-up voltage) is applied to the two lines of the serial clock line SCL and the serial data line SDA through respective pull-up resistors.
In a mobile communication terminal having a camera module, the communication between a main digital signal processor DSP of the mobile communication terminal and the camera module is carried out through the I2C bus. In this case, the main DSP serves to as a master device of the I2C bus, and an image sensor (or an image signal processor: ISP) of the camera module serves to as a slave device of the I2C bus.
FIG. 2 is a block diagram schematically illustrating a mobile communication terminal having a conventional camera module for performing communication using the I2C communication method.
As shown in FIG. 2, the conventional camera 11 for performing communication using the I2C communication method is mainly employed in a mobile communication terminal having a camera function, and in this case, the conventional camera 11 communicates with the main DSP of the mobile communication terminal through the I2C bus. Generally, a semiconductor device has diodes, provided at input and output terminals of the semiconductor device, for preventing the semiconductor device from being damaged by overcurrent due to electrostatic discharge ESD. In the camera module 11 and the image sensor unit 112 (or ISP, in this patent application, it is assumed that the image sensor unit 112 includes the ISP) in FIG. 1, diodes 113a and 113b for interrupting the overcurrent are connected between the serial clock line SCL and the serial data line SDA and the image sensor unit 112. These diodes 113a and 113b may be included in the image sensor unit 112.
As described above, when the camera function is not used, a source voltage Vcm is 0V by a power down signal provided from a main circuit 12 of the mobile communication terminal and the camera module 11 connected to the I2C bus stops the operation of the image sensor unit 112. At that time, due to characteristics of the diodes 113a and 113b that are connected to the serial clock line SCL and the serial data line SDA of the I2C bus for the purpose of preventing the overcurrent from being transmitted to the I2C bus, leakage currents Il1 and Il2 are supplied from an I2C pull-up power source Vdd to the image sensor.
Thus, the conventional camera module 11 for performing the communication using the I2C communication method generates the leakage currents through the serial clock line SCL and the serial data line SDA of the I2C bus at the stopped state when the power source is interrupted to stop the operation of the camera module.
Moreover, there is another method of stopping the operation of the camera module using a power down (PWRDN) input signal supported by the image sensor when the electric power is supplied to the camera module. This method may also generate current consumption of several tens to several hundreds of μA and consumes undesired current in comparison with the method of interrupting the power supplied to the camera module.